The present invention relates to a sprinkler head adapted to spread water to extinguish fire.
A sprinkler head includes a valve element sealingly held against a valve seat by a thermally responsive assembly. In the event of fire, the thermally responsive assembly collapses at an elevated temperature. This causes the valve element to drop and separate from the valve seat whereby water is sprayed. The thermally responsive assembly is devised so that an easily fusible alloy will melt in the event of fire to thereby cause structural parts of the thermally responsive assembly, supported by the fusible alloy, to be displaced to enable complete disruption of the thermally responsive assembly.
The sprinkler head is typically mounted on the ceiling of a building during construction and will not be removed until the building is intentionally destroyed due to age, except that the building suffers from fire. The valve seat is thus subjected to pressure for a prolonged period of time. Normally, water having a pressure of approximately 10 kgf/cm.sup.2 is filled in a pipe to which the sprinkler head is connected. To withstand such a high water pressure, the valve element is pressed against the valve seat with a significant amount of force to provide a tight seal and prevent water leakage. This force also acts on the thermally responsive assembly. As the thermally responsive assembly is of an intricate construction as previously described, its structural parts are prone to deformation or displacement due to material creep upon extended application of substantial force. As this occurs, a force under which the valve element is pressed against decreases, resulting in water leakage.
To this end, the sprinkler head includes means for reducing the extent of a force applied from the valve element to the thermally responsive assembly. This means utilizes the principle of a lever. That is, the amount of a force times the distance between the load and the fulcrum is equal to the amount of a force times the distance between the effort and the fulcrum. The greater the distance between the fulcrum and the load, the less force needs to be applied to the load.
A conventional sprinkler head employs a pair of bent levers as disclosed in Japanese patent publication No. 58-36985. Each of the levers is made of a flat plate and has a fishhook-like section. A substantial force is applied to a bent portion or apex of the lever which serves as the effort of the lever. The lever has a hook or short leg, the end of which serves as the fulcrum. The lever also has a long leg, the end of which serves as the load. The distance between the fulcrum and the load is greater than the distance between the effort and the fulcrum. Accordingly, only a small force is applied to the end of the long leg or a thermally responsive assembly.
To press a valve element, a substantial force is applied equally to the apexes of the two levers.
If a person walks with a long object or a small child throws an object in a room or hallway where a sprinkler head is installed, such objects may accidentally contact with the sprinkler head. It is likely that such contact of objects with the sprinkler head (referred to as "external force") will cause displacement or breakage of the thermally responsive assembly. As this happens, a force under which the valve element is pressed against decreases. This results in water leakage. In some cases, the valve element may be completely disengaged from the valve seat to thereby cause undesirable water discharge or explosion.
The valve element should be opened to discharge water only in the event of a fire. The water discharge inevitably dampens official machines, valuable documents, furniture, carpet or other interior objects. However, it will be a tremendous loss if this occurs due to inadvertent water leakage or explosion from the sprinkler head rather than actual fire.
In the prior sprinkler head, the thermally responsive assembly is likely to malfunction upon application of even a small amount of external force and create water damage. Full collapse of the thermally responsive assembly takes place when the fusible alloy melts to allow the levers to move. This arrangement also results in an increase in the number of necessary parts and the production cost, and requires substantial effort to fabricate the thermally responsive assembly.
The present invention provides a reliable and economical sprinkler head which is capable of holding a thermally responsive unit against displacement or breakage which may occur when external forces are applied, and which enables a reduction in the number of parts required to fabricate the thermally responsive unit and thus, the production cost.